title: Barley metallothioneins differ in ontogenetic pattern and response to metals.
abstract: The barley genome encodes a family of 10 metallothioneins (MTs) that have not previously been subject to extensive gene expression profiling. We show here that expression of MT1a, MT2b1, MT2b2 and MT3 in barley leaves increased more than 50-fold during the first 10 d after germination. Concurrently, the root-specific gene MT1b1 was 1000-fold up-regulated. Immunolocalizations provided the first evidence for accumulation of MT1a and MT2a proteins in planta, with correlation to transcript levels. In developing grains, MT2a and MT4 expression increased 4- and 300-fold over a 28-day-period after pollination. However, among the MT grain transcripts MT2c was the most abundant, whereas MT4 was the least abundant. Excess Cu up-regulated three out of the six MTs expressed in leaves of young barley plants. In contrast, most MTs were down-regulated by excess Zn or Cd. Zn starvation led to up-regulation of MT1a, whereas Cu starvation up-regulated MT2a, which has two copper-responsive elements in the promoter. Arabidopsis lines constitutively overexpressing barley MT2a showed increased sensitivity to excess Cd and Zn but no Cu-induced response. We suggest that barley MTs are differentially involved in intracellular homeostasis of essential metal ions and that a subset of barley MTs is specifically involved in Cu detoxification.
authors.affiliation: Plant and Soil Science Section, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, 40 Thorvaldsensvej, DK-1871, Frederiksberg C, Copenhagen, Denmark.
authors.forename: Michaela
authors.initials: M
authors.lastname: Schiller
authors.forename: Josefine N
authors.initials: JN
authors.lastname: Hegelund
authors.forename: Pai
authors.initials: P
authors.lastname: Pedas
authors.forename: Thomas
authors.initials: T
authors.lastname: Kichey
authors.forename: Kristian H
authors.initials: KH
authors.lastname: Laursen
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D002104:Cadmium / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D018525:Germination / Q000187:drug effects; D001467:Hordeum / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D008668:Metallothionein / Q000378:metabolism*; D019216:Metals, Heavy / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
chemical_list: D019216:Metals, Heavy; D010940:Plant Proteins; D002104:Cadmium; D003300:Copper; D008668:Metallothionein; D015032:Zinc
keywords: Cadmium; copper; gene expression; immunolocalization; metals; overexpression; zinc